This invention relates to means for driving reciprocating members, and more particularly, to the above described means, which is adapted to be for use in an electrophotographic copying machine of the scanning exposure type (i.e. a copying machine of the optical system transfer type and a copying machine of the manuscript platform transfer type).
According to the conventional arrangements, reversal of the drive of a movable member from a forward direction to the reverse, and vice versa, is effected by actuating a clutching means at an instance when the velocity of the forward, or the reverse movement of the movable member becomes zero. However, according to such actuating mode of the clutching means as described above, the movable member is gradually accelerated from a velocity of zero and then, attains a steady, optimum velocity of V for exposure after travelling a distance of Q, the situation of which is specifically shown in FIG. 1. Such being the case, since the movable member must travel an extra distance prior to the operation thereof, the resultant machine requires a relatively long copying time, accordingly. In addition, the resultant machine itself can not help being bulky in size. From the standpoint of the constructional arrangement, since the movable member must be accelerated from the velocity of zero, an initial torque and associated loads exerted on driving system including the clutching means must become large. Therefore, when the durability of the driving system is taken into consideration, the driving system further becomes bulky in size, with an accompanying high manufacturing cost.
To overcome such deficiencies as described above, the introduction of driving means having a high driving rating may be considered. However, this also results in the bulky size of the machine, with an accompanying high manufacturing cost thereof. Moreover, if such driving means as described above is introduced, an excessively rapid increase of the initial velocity as shown in a dot and line curve (b) in FIG. 1 causes unsteady vibration to take place in the copying machine. Furthermore, the increase of the initial velocity may not always bring the velocity to the predetermined level in an effective manner owing to the overshoot of the velocity as shown in FIG. 1. Thus, the conventional arrangements and such improvements as described in the foregoing can hardly solve the deficiencies as described earlier.
Recently, in view of the conventional deficiencies as described earlier, there have been proposed several improvements with respect to the means for controlling the movable member of the copying machine, which reciprocates in the forward and reverse directions to scan an original in cooperation with a resilient member e.g. a spring member. Namely, according to these proposals, the conversion of the reciprocating movement from the forward to the reverse is arranged to be smoothly executed through the resiliency of the spring member, which is located at one end of either the forward, or the reverse movement.
More specifically, according to a manuscript platform transfer controlling apparatus, which is disclosed in Japanese Laid Open Utility Model Application 52-55255, the manuscript platform is provided with a guide rod and a coil spring member coupled to the guide rod, while a stop is provided for the frame of the copying machine at a position where the scanning movement of the manuscript platform is executed, so that the guide rod and the coil spring member are resiliently engageable at the end of the scanning operation. The scanning movement of the manuscript platform is resiliently prevented from the further movement through the compression of the coil member at the end position and then the manuscript platform is adapted to begin the reverse movement through the resilient force prior to the actuation of the clutch for the reverse movement. Similarly, according to an arrangement disclosed in Japanese Laid Open Utility Model Application 54-82636, there is also provided a buffer stopping means. The buffer stopping means comprises a resilient member, being positioned at a position of the reversal of movement of the reciprocating member and being compressible at the position, and a clutch arrangement capable of changing over the direction of the reciprocation in cooperation with the resilient member, wherein respective actuations of the cessation of the forward movement and the start of the reverse movement are arranged to be executed, after the resilient member has been compressed. In spite of the improvements in the prior art as described above, these arrangements can only buffer the momentum associated with the reciprocation and still have the following deficiencies. Namely, since the spring member per se is provided either for the scanning member or at the end of the scanning movement, the consequent arrangement can not help being complicated. In addition, as for the most undesirable point, the movable member must perform a full scanning step, even if the lengthwise size of the original is smaller than the distance of the full scanning movement. This is due to the fact that in either of the arrangements, since the spring member of the stop is selectively provided at the position where the full scanning movement ends, the movable member must travel the full scanning movement, irrespective of the size of the original. Accordingly, as long as these arrangements are employed for the purpose as described earlier, rapid, continuous electrophotographic reproductions can not be made. On the other hand, according to a copying apparatus disclosed in U.S. Pat. No. 4,192,608, in order to execute the change of movement to return the movable member to the position of the start of the scanning movement, the apparatus takes advantage of the resilient character of a spring member. However, according to the known apparatus as described above, the spring member must be provided at approximately the end position of the return movement of the manuscript tray. In addition, the apparatus described above further requires movement restriction means so as to permit the spring member to be maintained in a compressed condition, even if a successive reproduction is not intended to be carried out. Thus, according to the arrangement, the apparatus of the arrangement consequently becomes complicated.